A/N: I seem to have this total obsession with setting myself crazy hard research projects in Time Lord matters, so today I present Tardisology. Everything here is according to The Whoniverse's TARDIS Technical Index website, with a couple of fun quirks thrown in so I can get cheap gags :P

I swear it's review reply time because I don't remember doing it for ages ... err, I think?

Chapter 10: The Holiday, Part Three

'Temperature 14 degrees celsius. Life signs normal. 4:59pm.'

'The next photo was Rose covered in mud, sitting on a swing,' Jack said.

'Yeah,' the Doctor said. 'It started with Leah's birthday. I'd promised to teach her a bit about the Tardis. It was the next part of Leah's Time Lady training. We'd done regeneration theory, bonding theory, we were working on regeneration practical, and now it was Tardisology.'

'Tardisology,' Jack repeated.

'That's what Rose called it,' the Doctor said. 'All the Tardis history and technical aspects. I started off by getting Leah in the console room and trying to explain the Tardis as I learnt about them when I was a kid …'

'... Rose couldn't resist watching.'

'Right,' the Doctor began, leaning on the console and looking at his daughter. 'So I know you know the basics. First of all, let's cover the technical aspects. Tell me what you know about a Tardis.'

Leah straightened up, clutching her notebook and looking proud. 'They were originally called TT capsules. They're designed for six pilots. A Tardis relocates itself in N-Space by travelling in the Fifth Dimension.'

'And what's the Fifth Dimension?'

'The vortex,' Leah replied promptly.

'So what are some of the features the Tardis uses to cope with the dangers of the vortex?'

'A Tardis uses Vortex Shields to protect itself and if it hits Time Spillages a pilot uses muon based counter-magnetisation to stop the Time Signature getting erased and the Tardis getting lost.'

Rose blinked in surprise and confusion at the stream of words coming out of her six-year-old.

The Doctor grinned. 'Good. what else?'

'Most of a Tardis' systems uses billions of simultaneous calculations called Block Transfer Mathematics.'

'Give me two core time travel equations.'

'E equals MC cubed, and, err, 76Zs equals EQ cubed,' she said after some slight hesitation.

'Do we have any limits?' the Doctor asked.

'Yeah, we can't go beyond the edge of creation, and we can't go far before Event One or Event Two.'

'Event One and Event Two are the creation and end of the Universe,' the Doctor advised a confused Rose, before looking back at Leah. 'So, how's she powered?'

'Artron energy. Tardises have a load of power sources, like the Universe itself, and the Eye of Harmony, connected by a node of morphologically unstable living organic matter.' She paused, reconsulting her notebook. 'Um, how do you power her without the Eye, now?'

'Since it's not possible to connect with the Eye of Harmony anymore, I've adapted her systems so she can draw power from the rift in Cardiff using the extrapolator. We've still got the node, but it's more ornamental now. The Eye of Harmony made sure you had power across multiple universes so you could easily hop between realities, but now Gallifrey's gone and we use the rift energy from this universe, that means she struggles for power in other universes.'

'Like when we crashed in the parallel world,' Rose recalled.

'Exactly,' the Doctor confirmed, nodding. 'Without the Eye of Harmony, she had no multi-dimensional power source. Essentially, she ran out of fuel,' he confirmed, and looked back at his daughter. 'What else do you know?'

'The interior of a Tardis is in a different dimension from the exterior, no matter where you are,' Leah replied.

'Wait, we're inside a different dimension even if we're parked in Torchwood?' Rose asked.

The Doctor nodded. 'Think of the Tardis like an onion. The skin exists in the dimension we know and love, but they are layers and layers of dimensions stacking through the ship. That's what makes her bigger on the inside - the transcendental dimensions. When you're in the Tardis you constantly cross dimensions though you're not aware of it, which are all compacted into an outer shell, held in place by these things called "dimensional dams". If they spring a leak, you're either going to be stretched across time and space like the biggest pancake ever, or compacted into a tiny single atom as you get crushed to death, unable to get out. And most of the time you won't even notice if she's sprung a leak. So it's basically a slow, painful death that you don't even notice happening until it's too late. Not even the Tardis can tell.'

'Err … are the Tardis' dimensional dams okay right now?' Leah wondered, looking a bit scared.

The Doctor clicked his tongue, contemplating. 'You know what? I haven't checked for ages. So, anyway …'

Rose and Leah looked at each other, wide-eyed.

'Anything else?' the Doctor asked Leah.

'Yeah. A Tardis can only live for a couple of hundred years.'

Rose looked at the Tardis console, which she was sure had to be much older than that. 'What?'

'That's not strictly true,' the Doctor said.

'But it was in the books,' Leah protested.

'A Tardis can live for thousands of years with lots of TLC,' the Doctor said. 'But usually on Gallifrey they were decommissioned after a few hundred years. It was easier and cheaper to get a new one than to keep maintaining an old one, plus you could get fancy new models, like iPhone upgrades, quite often.'

'How old is our Tardis?' Leah asked.

'Ask a rude question,' the Doctor joked as the lights appeared to pulse around them. 'I don't know. What I do know is the first Type 40s were created around five thousand years before the Time War. Obviously factor in my linear timeline, my best guess is she's around one and a half thousand years old.'

'What happened to Tardises that died, then?' Rose wondered.

'They were "put to sleep" by their pilots by linking it to another Tardis and piloting it into the heart of a star,' the Doctor replied. 'Once there, the Tardises use the energies of the star to get to the Tardis graveyard.'

'There's a graveyard for Tardises?' Rose asked.

'Yeah. Well, there was. Not sure if it's still there. Not a lot of people saw it anyway, it's very hard to get to. Okay. What else, Leah?'

'There were loads of different Tardis types on Gallifrey,' Leah said. 'But there wasn't much in the books about that.'

He nodded. 'The types were developed and enhanced over the years by gallifreyan engineers. Back on Gallifrey, we had Tardises used for scientific research labs, commercial Tardises, war Tardises, Tardises for your daily commute to the Panopticon, Tardises for moving around food and livestock, even taxi Tardises after your nights out in the Low Town. Our Tardis is a Type 40. Your basic, run-of-the-mill, common or garden, standard issue, typical, ordinary, middle-of-the-road … OW!'

He yelped and quickly withdrew his hand from the console from the mild electric shock that the TARDIS had evidently just given him.

'Let me finish!' he protested to his time machine, sucking his burnt fingers. 'I was saying, she's from common stock, yes, but our Tardis is really, really special. We'll get to that.'

The TARDIS almost seemed to purr at that.

'There have been at least 160 types of Tardis, all versions with varying degrees of success,' he continued, shaking out his fingers. 'Some were dangerous, some were useless, some were fine, others have had a complete mind of their own, ran away, and are probably still warping around the Universe some place. Some were extremely advanced, to the point of looking and acting like humanoids.'

'Wait a minute, how did you get inside the humanoid Tar …' Rose began with a frown, and then quickly stopped herself and held up her hands, glancing at the six-year-old. 'Okay, don't wanna know.'

The Doctor smirked. 'By the end of the war, you even had Tardises physically giving birth to Tardises - they became that complex. But originally, they were grown from a seed or a cutting.'

'How was our Tardis grown?' Leah wondered.

'Err, not sure, actually,' he confessed. 'Probably a seed ... A really beautiful, strong seed, full of seedy goodness,' he added loudly, side-glancing at the console.

She seemed to purr again.

'Despite having all these different types, every Tardis is unique, and the later types were definitely sentient. All the Type 40s I've known have been more like machines, though, which is why our Tardis is extra special. She's definitely sentient …' He waved his minorly burnt fingers to illustrate his point. '... With a personality, and likes and dislikes, including liking and disliking people. Some say that Tardises can even talk to each other, and chat and gossip. You've got to think of the Tardis as less like a machine, and more like a person. If something's wrong with her, she doesn't need parts fixing, she needs organs healing. She needs tender loving care, not brake oil. Although actually, that helps too.'

'You're her doctor,' Rose realised, grinning.

He smiled. 'Yeah. Speaking of, Tardises have a, err …' He reached to the console again, slightly warily, and touched her with her fingers. She didn't seem to mind, so he got a bit more confident and patted her. '... A special bond with their pilot. It's like she's part of me, and I'm part of her.'

'The symbiotic nuclei,' Leah stated. The Doctor nodded.

'What's that?' Rose asked.

'When I went to the Time Academy and became a Junior Time Lord, my biodata was altered to include what we call the symbiotic nucleus, which basically makes me biologically a Time Lord and also able to connect with a Tardis. It's insides my hearts. If it was ever taken out of me, that would kill me. The symbiotic nucleus lets you connect with a Tardis to form a semi-instinctual neural link. Essentially, we're woven into each other. She needs dematerialisation codes that are hardwired into my genetics. She can't function without me, and I can't be a Time Lord without her. That's why if I'm ill or if our connection is disrupted somehow, she struggles a little, and vice versa. The connection is so strong that Tardises have been known to kill themselves if their pilot dies with no regeneration, committing suicide by voluntarily flying into the heart of a star through sheer grief.'

'When did you get our Tardis?' Leah wondered.

'Ah,' the Doctor said, looking a bit awkward. 'Well, originally, a Tardis actually chose her pilot when you were still a Junior Time Lord at the Academy. My first Tardis was a Type 50. Then when I needed to leave Gallifrey, I knew I couldn't take my Tardis, so I went down to where they were storing the Tardises about to be destroyed, and stole one. This one,' he said.

'You just left your first Tardis?' Rose asked seriously.

'I had to,' the Doctor replied. 'And she wasn't happy that I did that. Actually, she ended up chasing me across the Universe. But that's a story for another day …'

The lighting in the console room suddenly seemed to get slightly redder.

'Hey,' the Doctor said to the rotor, patting the console again. 'You're the only one for me.'

The red light seemed to dull.

'Being sentient isn't the only reason she's special, though,' the Doctor continued. 'Every Tardis before the Type 65s could only be safely operated by their chosen pilot. If anyone else without a symbiotic nucleus tried, their DNA helix would split open. But - and I don't know how - our Tardis has found a bypass for that, so anyone can operate her if they know how. Our Tardis can also help, using the telepathic circuits to get an idea of where you want to go, and make sure you get there by subtly encouraging you to press the right buttons. But in order to do that, you have to put your faith in your "gut instinct", because that's how she's telling you what to do.'

'Wow,' Rose said, gazing at the rotor.

'So, what are some of her on-board features?' the Doctor asked Leah.

'The Tardis has a low level telepathic field, which translates languages, and also reads your surface thoughts.'

He nodded again. 'Good. It helps her to adapt to what we want and need. Like as I said, she can help non-pilots to get to where they want to go. Or, if I'm bursting for the loo, she can put the toilet directly in front of me. Or a mile down the corridor, depending on how annoying I've been.'

The buttons on the console flashed in a cascade.

'She has day and night cycles taken from the brainwaves of the passengers, and she plays music all the time to keep passengers calm and relaxed,' Leah stated, reading from her notebook.

Rose blinked, pausing to listen. 'She does?'

The Doctor smiled. 'Humans tell me it sounds like humming.'

'Really?' Rose asked, looking at Leah. 'Can you hear music?'

'Yeah, it sounds like a music box thing,' Leah replied. 'Can't you hear it?'

'No. Just me then,' Rose moaned. 'I thought that was just engines.'

'Nope,' the Doctor said. 'Just her, singing, if you like, trying to keep us all in a good mood on a subconscious level.'

'There's also an auto cleaning function,' Leah stated.

'Yeah. Unfortunately, as I've discovered in recent years, that doesn't seem to work on baby food or finger paint,' the Doctor lamented.

Rose giggled. 'Why not?'

'Well, she's supposed to wipe out all the excess particles of dust, mud, and debris, but obviously to do that, she needs to know the atomic and subatomic structure of all materials to safely remove them. Obviously, this database has to be limited to realistic ideas of the dirt that might gather in a Tardis …'

'... And the gallifreyan engineers decided that baby food and finger paint wasn't gonna be a problem?' Rose completed, smirking.

'Apparently not,' the Doctor said, shrugging. 'Next?'

'The Tardis Type 40 has, like, every room you could ever want,' Leah said. 'If you gave a guided tour it would take a year to see everything.'

'Yep. Also, if the dimensional structure is unstable or damaged somehow, you can get rooms falling into rooms,' the Doctor said. 'One day you might wake up and find your bedroom's fallen into the library. You can also jettison rooms. I had to flush out the swimming pool after it got a leak, once. That was a bit messy.'

'Probably was,' Rose mused.

'Okay, that's everything for today,' the Doctor told Leah.

Leah's face fell. 'But can't I pilot her?'

'No.'

'Why?' she moaned.

'We haven't even got anywhere near covering the Dynamorphic Generators, the Anti-Collision Control, or even any dematerialisation precautions, yet.'

'But I've flown her before!' Leah whined.

'The last couple of times you've flown her I've had to gut out the gravitic anomaliser from the amount of time grime you've managed to leave behind.'

'Time grime?' Leah repeated, confused.

'It's this brown gooey stuff that gets on the filter.'

'Do you mean the gravitic backwash?' Leah said, checking the notes she'd made.

Rose sniggered a little.

The Doctor scratched his head. 'You know what, Leah, in this Tardis, it's called time grime.'

Leah frowned. 'But it's called …'

'Anyway!' the Doctor interrupted in a high-pitched voice. 'Lesson over. We'll resume another day.'

'But I wanna fly!' Leah complained.

'No, you …'

'Daddy!' she said, immediately assuming her "adorable" pose, looking up at him under her long, fluttering eyelashes with her fists bunched into her shirt.

The Doctor immediate covered his face to avoid looking into his six-year-old's cute and strangely hypnotic eyes. 'No.' He stated firmly.

'Pleeease?' she said, tugging on his trousers.

'Nooooo,' he replied in the same tone of voice.

'Pleeeeease?'

'Noooooo.'

'Pleeeeease? It's my birthday.'

'No.'

'Oh, for god's sake, let her fly,' Rose complained.

The Doctor sighed, and dropped his hands. 'Okay, okay,' he said, stepping back and gesturing to the console. 'Off you go.'

'Yay!' Leah chimed, and began scooting around. The Doctor dropped to sit next to Rose on the pilot's chair, folding his arms. Leah still wasn't quite tall enough to reach the very top buttons and levers.

'So where are we going?' the Doctor asked.

'Dunno,' Leah said, and with a bit of effort, pulled down the handbrake. The Tardis juddered and shook, and the parents had to quickly grab onto the seat to keep from crashing to the floor.

'Careful!' the Doctor complained.

'What? You always do that,' Leah told him as finally the time rotor began to pump and the shaking stopped.

'She's right,' Rose told the Doctor, sticking her tongue out at him.

'Temperature 15 degrees celsius. Life signs normal. 5:10pm.'

They were suddenly interrupted by the sound of distant, muted footsteps - specifically, high heels on stone. Immediately Jack started to panic.

'Shit, shit. Play possum. Don't open your eyes for anything,' he ordered the Doctor, and after a scuffle he went quiet. The Doctor obeyed, closing his eyes and falling limp.

A heavy metal door opened, scraping across the stone floor. The footsteps continued, closer. Then, they stopped, right outside his cell.

He heard the sound of the forcefield drop, and then the footsteps moved up behind him, very close. He kept his eyes firmly closed as the overwhelming smell of sandalwood washed over him. He wanted to open his eyes to see who it was, but Jack's panicked warning convinced him to stay limp.

The person moved around to his front. He then felt hot breath on his face as they leant in, seemingly centimetres away from him. Hands clasped his cheeks, and he could feel long fingernails lightly scraping the stubble he'd grown on the bottom of his chin. one of the nails lingered perilously close to the main artery in his neck, like some kind of warning. This person knew gallifreyan anatomy.

He felt the fingers move up to his temples. Was this person telepathic? He didn't have time to decide, so he quickly put up as many mental barriers as he could to shield himself from any mental intrusion.

After a few seconds, the hands dropped. A pause, as he thought they were about to leave. Then the person suddenly blew a sharp breath onto his face. Shocked a little, he couldn't help but flinch. Had they noticed?

He heard a giggle, which sounded more like a purr. Now he knew for sure that it was a woman, and that she knew he was pretending.

To his utter astonishment, she didn't do anything with that information. She simply walked away, back across the cell as the smell of sandalwood disappeared. The forcefield came back up, and the clip-clop of high-heels eventually faded away.

'Shit, thank god,' Jack muttered. 'She didn't do anything, did she?'

'No,' the Doctor replied, opening his eyes again to meet the same, upside-down grotty wall. 'Who was that? Cruella de Vil?'

Jack laughed. 'Oh, yeah,' he realised, 'you've got no idea, have you?'

'No. She really overloads on the perfume, though.'

'We'll get to that part. Where were we?'

'Tell me who that was and why you're so scared.'

'I told you, we'll get there.'

'How about now?'

'How about no?'

The Doctor sighed. 'Tell me, before I remember, how much do I actually like you?'

Jack laughed. 'Anyway. Where did we get to?'

'No,' the Doctor said firmly. 'No more stories until you tell me what's going on and where Rose, Leah, and Theo are.'

'For the millionth time, I can't.'

'Please, Jack.'

'No. You have to trust me, Doctor. Please, please trust me. Because we've haven't got much time left.'

'Until what?'

'Until Rose, Leah, and Theo won't be very safe at all.'